It is known that a conventional aromatic imide polymer laminate material comprising an aromatic imide polymer film and a metallic foil is produced by bonding an aromatic imide polymer film produced from a reaction product of pyromellitic dianhydride with an aromatic diamine to a metallic foil, for example, a copper foil, with a thermo-resistant bonding agent and is usable as a substrate for printed circuit board.
In the preparation of the conventional aromatic imide polymer laminate material, it is necessary that the bonding agent exhibit a satisfactory heat resistance and an excellent bonding activity. Conventional bonding agents are, however, extremely expensive and unsatisfactory in respect to the heat resistance, chemical resistance, moisture resistance, and flexibility thereof. Therefore, when a conventional bonding agent is used to bond the aromatic imide polymer film to the metallic film, the resultant bonding layer forms a weak portion in respect to the heat resistance, chemical resistance and moisture resistance of the laminate material.
Various attempts have been made to directly bond the aromatic imide polymer film to the metallic foil by means of a heat-pressing procedure without using a bonding agent. However, such attempts have been unsuccessful because the conventional aromatic imide polymer prepared from pyromellitic acid exhibited an extremely poor bonding activity in regard to the metallic foil. Even when the pyromellitic acid-type imide polymer film was directly bonded to the metallic foil, the resultant laminate material did not exhibit a satisfactory bonding strength to the extent that the laminate material could be actually used as a printed circuit board.
Therefore, an aromatic imide polymer film which is capable of being bonded to the metallic foil by means of a heat-pressing procedure without using a bonding agent is greatly desired.